This work aimed to discover targets for combination treatment with
gemcitabine in
pancreatic cancer. We selected 11
tumors from our live collection of freshly generated
pancreatic cancer xenografts with known degrees of varying
gemcitabine sensitivity. We briefly (6 h) exposed fine-needle aspiration material to control vehicle or
gemcitabine (1 mumol/L) and compared the gene expression of the treated and untreated samples using a reverse transcription-PCR-based, customized low-density array with 45 target genes of therapeutic interest. The gene expression of the untreated sample (which can be considered a baseline/static readout) was not predictive of
gemcitabine efficacy in these
tumors. Altogether, the only gene that differentiated sensitive versus resistant cases was
polo-like kinase 1 (Plk1), showing >50% downregulation in sensitive cases and no change in the resistant cases. Inhibition of Plk1 by either
small interfering RNA gene knockdown or with the Plk1 pathway modulator (
ON 01910.Na) synergized with
gemcitabine in
gemcitabine-refractory in vitro models providing mechanistic proof of concept. In vivo experiments in
gemcitabine-resistant xenografts showed synergistic activity decreasing cell proliferation and
tumor regressions. A quantitative gene expression-based vulnerability assay identified Plk1 as a relevant target dictating the susceptibility of
pancreatic cancer to
gemcitabine. Dynamic interrogation of
cancer has the potential to provide key information about mechanisms of resistance and to enhance individualization of treatment.